The present invention relates to a muffle for a furnace and to a method for making such muffles from ceramic fibers.
Muffle furnaces are widely used because of the high temperatures, accurate control characteristics, speed and convenience which they afford. It is necessary to provide insulation about the heating elements of the furnace to ensure that the interior chamber of the furnace provides the temperature necessary and maintains constant temperature. Hence, a characteristic necessary for safe and efficient muffle furnace operation are walls which include insulation material of substantial thickness and good insulating properties. For example, on the average, the insulation in a typical muffle will have a thickness of approximately 2 inches.
In addition to providing adequate insulating capabilities, another important requirement for a muffle wall is that it be structurally stable. Hitherto, muffles have generally been fabricated by assembling five blocks of insulation in a spatial, self-supporting manner to create a box with an open end to define the chamber for the oven. The blocks of insulation to be self-supporting must be assembled together using a refractory cement applied between abutting surfaces of the blocks. This process takes time and adds to the overall cost of the product. In addition, the insulation blocks must be assembled in such a manner as to accommodate the thermal expansion and contraction resulting from very wide temperature ranges. Thus, the end connections between the insulation blocks must accommodate the thermal expansion, and this may affect the inherent stability of the muffle structure. An example of such a prior art muffle assembled in this manner is disclosed in U.S. Pat. No. 3,749,882 issued to Pilkington et al. on Jul. 31, 1973.
As a result, there have been efforts to mold a muffle in one piece in a vacuum mold using a form, upon which a slurry is deposited. Such one-piece muffles have been found to be relatively vulnerable to imports and other stresses.
Accordingly, it is an object of the invention to provide a novel muffle which is formed as a unitary member and which is relatively rugged in construction and self-supporting.
It is also an object to provide such a muffle with structural features which facilitate its stable seating in a furnace.
Another object is to provide a novel method for making such a muffle from ceramic fibers and which is economical and relatively simple to practice.